1. Field of the Invention
The present invention relates to a coding and multiplexing apparatus and method and more particularly, is suitably applied to a transmission system for a digital multichannel broadcasting.
2. Description of the Related Art
Digital multichannel broadcastings using a communication satellite (CS) have been started even in Japan. Moreover, in the near future, a similar service will be provided in broadcasting systems using a broadcasting satellite (BS), and ground waves or cables.
Such digital multichannel broadcasting is performed in such a manner that, in a transmitting side, a video signal of each channel is subjected to a digital compression processing and obtained coded data is transmitted after being multiplexed within a limited band (hereinafter, this is referred to as broadcast bandwidth), for instance, of 30 bps degree.
FIG. 1 shows a structural example of the transmitting side in such the digital multichannel broadcasting system. In such a transmission system 100, a plurality of coding devices 102A to 102N are provided, in which video signals S101A to S101N are supplied to the coding devices 102A to 102N respectively.
Each of the coding devices 102A to 102N performs compression coding on the supplied video signal S101A to S101N, for example, at a peculiar set rate preset based on the moving picture experts group phase 2 (MPEG2), and transmits thus obtained coded data D101A to D101N to a multiplexer 103. Note that, the set rate for each coding device 102A to 102N has been set so that the total of the set rates is within the broadcast bandwidth of the digital multichannel broadcasting.
In the multiplexer 103, a plurality of buffers 104A to 104N provided corresponding to coding devices 102A to 102N respectively and a multiplexing control part 105 for controlling read-write of each buffer 104A to 104N are included. The coded data D101A to D101N supplied from coding devices 102A to 102N respectively are sequentially fed into the corresponding buffers 104A to 104N.
Besides, the multiplexing control part 105 monitors the amount of data in each buffer 104A to 104N via a control bus 106, and evenly reads the coded data D101A to D101N from respective buffers 104A to 104N in time division based on the monitor result.
As a result, these coded data D101A to D101N, respectively read from respective buffers 104A to 104N, are supplied to a transmitting part 108 via a data bus 107 as transmission data D102. In the transmitting part 108, the transmission data D102 is subjected to a predetermined signal processing, such as quadrature phase shift keying (QPSK) modulation, and then transmitted to a receiving side sequentially via an antenna 109, a communication satellite not shown in the figure, and the like, as a transmission signal S102.
The fixed rate method of coding each of the video signals S101A to S101N for a plurality of channels at a rate preset for each channel has an advantage that the coded data D101A to D101N corresponding to the video signals S101A to S101N can be multiplexed in time division within the broadcast bandwidth without requiring complicated control.
However, the fixed rate method as described above has a problem in that pictures are greatly inferior in quality in complicated pictures or in changing scenes because the video signal A101A to A101N of each channel is always digital-compressed at a fixed rate.
In addition, the fixed rate method has a problem in that transmission efficiency deteriorates because dummy data has to be added to a picture which needs only a few amount of code in order to keep the output rate constant.
To solve the problems, a statistics multiplexing method has been proposed as another method of coding and multiplexing video signals S101A to S101N for a plurality of channels.
FIG. 2 in which the same reference numerals are applied to parts corresponding to FIG. 1 shows a structural example of a transmission system 200 for performing coding and multiplexing in accordance with the statistics multiplexing method. A plurality of coding devices 202A to 202N are provided so as to be given video signals S101A to S101N respectively.
In this case, each of the coding devices 202A to 202N is composed of a coding-difficulty detecting parts 212A to 212N and a coding part 213A to 213N, so as to input the supplied video signal S101A to S101N to the coding-difficulty detecting part 212A to 212N. Then, the coding-difficulty detecting part 212A to 212N detects difficulty of coding the supplied video signal S101A to S101N, and transmits the obtained difficulty information D210A to D210N to a multiplexer 203 and the video signal S101A to S101N to the coding part 213A to 213N of the next stage.
The multiplexer 203 includes a plurality of buffers 204A to 204N respectively corresponding to the coding devices 202A to 202N, a multiplexing control part 205 for controlling write-read of each buffer 204A to 204N, and a coding control part 215 for controlling the coding parts 213A to 213N of the coding devices 202A to 202N. The difficulty information D210A to 210N supplied from the coding-difficulty detecting parts 212A to 212N of the coding devices 202A to 202N are input to the coding control part 215.
The coding control part 215 decides coding rates for the coding devices 202A to 202N based on the respective difficulty information D210A to D210N so that a video signal S101A to S101N having larger difficulty can use a wider bandwidth and the total of coding rates is within the broadcast bandwidth for the digital multichannel broadcasting. Then, the coding control part 215 transmits control signals S210A to S210N based on the derision result to the coding parts 213A to 213N of the coding devices 202A to 202N respectively.
Thus, the coding parts 213A to 213N of the coding device 202A to 202N code the respectively-supplied video signals S101A to S101N at respective coding rates, which are obtained based on the. control signals S210A to S210N supplied from the coding control part 215 of the multiplexer 203. Each of the obtained coded data D201A to D201N is transmitted to the multiplexer 203.
As a result, the coded data D201A to D201N, which are output from the coding devices 202A to 202N respectively, are fetched to the corresponding buffers 204A to 204N of the multiplexer 203, are evenly read out in time division under the control of multiplexing control part 205, and then, are transmitted to a transmitting part 108 through a data bus 207 as transmission data D202. The transmission data D202 is subjected to a predetermined signal process in the transmitting part 108, and then is transmitted to the receiving side sequentially via the antenna 109, a communication satellite not shown in figure, and the like, as a transmission signal S202.
Such the statistics multiplexing method has an advantage in that, as compared with the fixed rate method, transmission efficiency is good and a picture having high difficulty can be transmitted remaining comparatively high quality on the average of picture quality among channels, because dummy data does not have to be added and the coding rate is decided based on the difficulty of a picture for each channel as described above.
However, the statistics multiplexing method has a problem in that simultaneous control of channels is complicated and it is difficult to make the best use of the merit of dynamically controlling bandwidth, in such a case that the same video signal is hierarchical-coded to be broadcasted on plural channels, because the amount of coded data changes depending on a picture.
Further, in the digital multichannel broadcasting, also materials, such as a movie, in which the contents have been already fixed are coded and broadcasted in real time at present. In this case, as one of the methods of coding and broadcasting such a material of which the contents have been already fixed, a method in which the material is coded and stored in advance to be broadcasted at a broadcast time can be considered. Such method has an advantage that more optimized coded data can be obtained comparing with the real-time coding processing because the material can be coded through a multipath.
To sufficiently make the best use of such merit, however, there are limitations in the fixed rate method. That is, in the fixed rate method, dummy data is added to a picture with less amount of code to fix each channel rate.
Therefore, the fixed rate method has a problem in that it is difficult to multiplex a plurality of coded data at a variable rate in which the amount of code has already fixed and the coded data obtained by the real-time coding within the limited broadcast bandwidth with high transmission efficiency.
Further, it is considered in the digital multichannel broadcasting that in a broadcasting station such as a local station and a cable television, programs transmitted from other stations are broadcasted on some channels and original programs are broadcasted on remaining channels.
Therefore, the broadcasting station such as a local station and a cable television needs a transmission system capable of multiplexing and broadcasting data of programs transmitted from other stations and data of original programs within the limited bandwidth.
FIG. 3 shows an structural example of such transmission system, in which a plurality of rate converters 302A to 302N and a plurality of coding device 312A to 312N are provided at a input stage. The rate converters 302A to 302N are given, for example, coded data D301A to D301N of programs transmitted from other stations respectively, and the coding devices 312A to 312N are given video signals S311A to S311N of original programs.
Each rate converter 302A to 302N converts a rate to a predetermined rate previously set for the channel (hereinafter, referred to as a set rate) with a method of decoding the supplied coded data D301A to 301N and coding it again or with a method of eliminating high hierarchical coefficients without decoding, in order to transmit obtained coded data D311A to D311N to a multiplexer 303.
Further, each coding device 312A to 312N compression-codes the supplied video signal S311A to S311N at the set rate for the channel, and transmits obtained coded data D321A to D321N to the multiplexer 303. Note that, the set rates of the channels are set in advance so that the total of them is within a bandwidth which can be used for the broadcasting station.
The multiplexer 303 is composed of a plurality of buffers 304A to 304N and 314A to 314N respectively corresponding to the rate converters 302A to 302N and the coding devices 312A to 312N, and a multiplexing control part 305 for controlling read-write of each buffer 304A to 304N, 314A to 314N.
In this case, the multiplexing control part 305 makes the buffers 304A to 304N and 314A to 314N take in the coded data D311A to D311N and D321A to D321N respectively, which are supplied from the rate converters 302A to 302N and the coding device 312A to 312N respectively, and moreover, sequentially reads each of the coded data from the buffer 304A to 304N and 314A to 314N in time division at a set rate of each channel.
As a result, the coded data D311A to D311N and D321A to D321N, which are read out from the respective buffers 304A to 304N and 314A to 314N, are supplied to a transmitting part 308 as transmission data D302. The transmission data D302 is subjected to a predetermined signal processing and is transmitted to a receiving side as a transmission signal S302.
In this way, the transmission system 300 can perform a digital multichannel broadcasting by multiplexing the coded data D301A to D301N supplied from other stations and coded data D321A to D321N obtained by coding the video signals S311A to S311N of original programs.
However, such the transmission system 300 has a problem in that a picture is greatly inferior in quality in a complicated picture or in changing scenes when the coding devices 312A to 312N compression-codes the video signals S311A to S311N, because a rate is fixedly assigned to each channel.
Further, the transmission system 300 has a problem in that transmission efficiency deteriorates because dummy data have to be added even to a picture which needs only a few amount of code at the time of compression-coding the video signals S311A to S311N in the coding devices 312A to 312N, since the rate is fixedly assigned to each channel to keep the output rate constant.
FIG. 4 shows an structural example of another digital multichannel broadcasting system. In a transmission system 400, a plurality of hierarchical coding devices 402A to 402N are provided so as to be given video signal S401A to S401N in the high definition television (HDTV) system respectively.
An information hierarchical part 410 of each hierarchical coding device 402A to 402N sequentially performs a filtering and a subsampling on the supplied video signal S401A to 401N to hierarchically generate a plurality of pictures having different resolutions. The plurality of pictures are taken as layer video signals S411A to 411M in the order of lower frequency component (that is, in the order of pictures having rougher resolution), and are supplied to corresponding layer coding parts 412A to 412M.
The layer coding parts 412A to 412M mutually obtain differences between layer video signals S411A to S411M through a data path 415 Thereby, the layer video signal S411A having the lowest frequency component, which is obtained by down-subsampling the video signal S401A, is supplied to the layer coding part 412A. And only the remaining component obtained by eliminating the frequency component of the layer video signal S411A from the layer video signal S411B is supplied to the layer coding part 412B. In the same way, as a layer becomes higher rank, only remaining frequency component being difference between the layer and the following low rank layer (that is, a part remaining after eliminating a correlation picture) is supplied to the layer coding part 412C to 412M, one after another.
Thus, each layer coding part 412A to 412M compression-codes the remaining component, which remains after eliminating a correlation component for each layer, of the supplied video signal S411A to S411M at a proper set rate previously set based on, for example, the moving picture experts group phase 2 (MPEG2), and transmits thus obtained layer coded data D411A to D411M to the corresponding layer buffer 414A to 414M. Note that, the set rates for the layer coding parts 412A to 412M in the each coding device 402A to 402M are set so that the total of the set rates is within a broadcast bandwidth in the digital multichannel broadcasting.
Each layer buffer 414A to 414M takes in the supplied layer coded data D411A to D411M under the control of hierarchical coding and multiplexing control part 418.
The hierarchical coding and multiplexing control part 418 monitors the amount of data in each layer buffer 414A to 414M through a control bus 416 to evenly read the layer coded data D411A to D411M from layer buffers 414A to 414M based on the monitor result in time division.
As a result, the layer coded data D411A to D411, which are read from the layer buffers 414A to 414M respectively, are given to a multiplexer 403 as coded data D401A through a data bus 417.
In the multiplexer 403, a plurality of multiplexing buffers 404A to 404N respectively corresponding to the hierarchical coding device 402A to 402N and a multiplexing control part 405 for controlling read-write of each multiplexing buffer 404A to 404N are provided. The coded data D401A to D401N supplied from the hierarchical coding device 402A to 402N respectively are taken in to the corresponding multiplexing buffers 404A to 404N.
The multiplexing control part 405 monitors the amount of data in each multiplexing buffer 404A to 404N through a control bus 406 to evenly read the coded data D401A to D401N from the multiplexing buffers 404A to 404N based on the monitored result in time division. As a result, the coded data D401A to D401N, which are read out from the multiplexing buffers 404A to 404N respectively, are given to a transmitting part 108 through a data bus 407 as transmission data D402. The transmission data D402 is subjected to a predetermined signal processing such the quadrature phase shift keying (QPSK) modulation in the transmitting part 108, and then is transmitted to a receiving side successively via an antenna 109, a communication satellite not shown, and the like, as a transmission signal S402.
The fixed rate method of coding the video signals S401A to 401N for a plurality of channels at a rate set in advance for each channel has a advantage in that the coded data D401A to 401N obtained by hierarchically layering the video signal S401A to S401N can be multiplexed in time division within a broadcast bandwidth without complicated control.
However, the fixed rate method as described above has a problem in that a picture is greatly inferior in quality in a complicated picture or in changing scenes because the video signal S401A to S401N for each channel is always subjected to the digital compression processing at a fixed rate. In addition, the fixed rate method has a problem in that transmission efficiency deteriorates because dummy data have to be added to a picture which needs only a few amount of code to keep an output rate constant.
To solve the problems, the statistics multiplexing method has been proposed as another method of coding and multiplexing the video signals S401A to S401N for a plurality of channels. This statistics multiplexing method is the method of detecting difficulty for the time of coding each video signal, and set a. coding rate for each coding device so that a wide band is assigned to a video signal having high difficulty and the total of coding rates is within a broadcast bandwidth for the digital multichannel broadcasting.
Such the statistics multiplexing method has an advantage in that, as compared with the fixed rate method, transmission efficiency is good and a picture having high difficulty can be transmitted remaining comparatively high quality on the average of picture quality of channels, because dummy data does not have to be added and the coding rate is decided based on difficulty of a picture for each channel as described above.
However, the statistics multiplexing method has a problem in that simultaneous control of channels is complicated and it is difficult to make the best use of the merit of dynamically controlling bandwidths, as in the case of the transmission system 400 shown in FIG. 4 in which that the same video signals S401A to S401N is hierarchical-coded to be broadcasted on plural channels, because the amount of coded data changes depending on a picture.
In view of the foregoing, an object of this invention is to provide a coding and multiplexing apparatus and a coding and multiplexing method capable of remarkably improving transmission efficiency.
The foregoing object and other objects of the invention have been achieved by the provision of a coding and multiplexing apparatus which comprises buffers for storing coded data output from corresponding coding means and multiplexing means for reading out and multiplexing each of coded data, which are stored in the buffers, in time division at a proper rate set in advance for corresponding coding means. The multiplexing means distributes a surplus bandwidth for a set rate of coding means among the read of the coded data from buffers corresponding other coding means.
As a result, in the coding and multiplexing apparatus, bandwidth control for each channel can be dynamically performed, and also a temporal change in difficulty in coding can be absorbed through channels.
Further, this invention provides the coding and multiplexing method comprising the first step of compression-coding video signals and storing the obtained coded data into different buffers, and the second step of reading out each of the coded data, which are stored into the different buffers, in time division at a proper timing preset for each channel. The second step distributes a surplus band for a set rate of a channel among the read of coded data from the buffers of other channels.
As a result, according to the coding and multiplexing method, a bandwidth for each channel can be dynamically controlled and temporal change in difficulty in coding can be absorbed through the channels.
Further, this invention provides the coding and multiplexing apparatus which comprises a plurality of the first buffers for respectively storing the first coded data read out from a storage means, a plurality of the second buffers for respectively storing the second coded data which are obtained by compression-coding video signals outputted from the corresponding coding means, and multiplexing means for reading out each of the first and second coded data, which are respectively stored in the first and the second buffers, in time division at a proper rate preset for the corresponding storage means or coding means and multiplexing the first and the second coded data. And the multiplexing means distributes a surplus bandwidth for the set rate of the storage means and the coding means among the read of the second coded data from the second buffers corresponding to the other coding means.
As a result, in this coding and multiplexing apparatus, the bandwidth for each channel can be dynamically controlled, and also a temporal change in difficulty in coding can be absorbed through channels.
Moreover, this invention provides the coding and multiplexing method which comprises the first step of reading the first coded data for one or a plurality of channels that has been previously stored after compression-coded and storing them in the different first buffers as well as performing the compression coding on inputted video signals for one or a plurality of channels and storing the second coded data obtained in different second buffers, and the second step of reading each of the first and the second coded data, which are respectively stored in the first and second buffers, in time division at a proper rate preset for each channel and multiplexing the first and the second coded data. In the second step, a surplus bandwidth for the set rate of each channel is distributed among the read of the second coded data of other channels from the second buffers.
As a result, according to the coding and multiplexing method, a bandwidth for each channel can be dynamically controlled, and also a temporal change in difficulty in coding can be absorbed through channels.
Further, this invention provides the coding and multiplexing apparatus which comprises first buffers for storing first coded data which is subjected to a rate conversion and is outputted from the corresponding rate conversion means, second buffers for storing second coded data obtained by compression-coding video signals outputted from respective coding means, and multiplexing means for reading each of the first and second coded data, which are stored in respective first and second buffers, at a proper set rate preset for corresponding rate conversion means and coding means. And the multiplexing means distributes a surplus bandwidth for the set rate of the rate conversion means and the coding means among the read of the first or second coded data from the first or second buffers corresponding to other rate conversion means or coding means.
As a result, in the coding and multiplexing apparatus, a bandwidth for each channel can be dynamically controlled, and also a temporal change of the amount of code in rate conversion or in coding can be absorbed through channels.
Further, this invention provides the coding and multiplexing method which comprises the first step of converting rates of inputted coded data for one or a plurality of channels and storing them in different first buffers as well as compression-coding video signals for one or a plurality of channels and storing them in different second buffers, and the second step of read each of the first coded data and second coded data, which are stored in the first and second buffers respectively, in time division at a proper set rate preset for each channel. And the second step distributes a surplus bandwidth for a reading rate of each channel among the read of the fist and/or second coded data from the first and/or second buffers corresponding to other channels.
As a result, in the coding and multiplexing method, a band for each channel can be dynamically controlled, and also a temporal change of the amount of code in rate conversion or in coding can be absorbed through channels.
Further, this invention provides the coding and multiplexing apparatus which has hierarchical means for converting an inputted video signal into a plurality of layer video signals which hierarchically have different resolutions and which compression-codes each of layer video signals, which are outputted from the hierarchical means with different coding means, and multiplexes the obtained coded data. The coding and multiplexing apparatus comprises buffers provided corresponding to the coding means for storing coded data outputted from corresponding coding means, and multiplexing means for reading each of coded data, which are stored in the buffers, in time division at a proper set rate preset for corresponding coding means and multiplexing the coded data. The multiplexing means distributes a surplus bandwidth for the set rate of the coding means among the read of coded data from the buffers corresponding to other coding means.
As a result, in the coding and multiplexing apparatus, a bandwidth for each layer can be dynamically controlled, and also a temporal change of the amount of code in coding can be absorbed through channels.
Furthermore, this invention provides the coding and multiplexing method for converting an inputted video signal into a plural layer video signals hierarchically having different resolutions, compression-coding each layer video signal, and multiplexing obtained coded data. The coding and multiplexing method comprises the first step of storing coded data of layers in respective buffers, and the second step of reading each of the coded data, which are stored in respective buffers, in time division at a proper set rate preset for each layer and multiplexing coded data. The second step distributes a surplus bandwidth for the set rate of the layer among the read of coded data from the buffers corresponding to other layers.
As a result, in the coding and multiplexing method, a bandwidth for each layer can be dynamically controlled, and also a temporal change of the amount of code in coding can be absorbed through layers.